An Etymological Dictionary of the German Language/bieder
bieder, adj., ‘staunch, honest,’ from MidHG. bíderbi, OHG. biderbi, ‘serviceable, useful,’ then ‘brave, gallant’ (comp. besser for a similar of idea); lit. ‘suitable to one's need or purpose,’ for the adj. is a compound of the stem of dürfen, ‘to he in need of,’ and the prefix bi, which has retained its earlier accent without being replaced, as it usually is, by bî. The Goth. form was perhaps *bíþarbs; further, the adj. is identical with derb.